Field of the Invention
The present invention relates to a toner, a developer, and an image forming apparatus.
Description of the Related Art
In recent years, toners have been required to have smaller particle diameters and hot offset resistance for increasing quality of output images, to have low temperature fixing ability for energy saving, and to have heat resistant storage stability for the toners to be resistant to high-temperature, high-humidity conditions during storage and transportation after production. In particular, improvement in low temperature fixing ability is very important because power consumption in fixing occupies much of power consumption in an image forming step.
Conventionally, toners produced by the kneading pulverizing method have been used. In the toners produced by the kneading pulverizing method, difficulty is encountered in making them have smaller particle diameters, and their shapes are indefinite and their particle size distribution is broad, for which these toners have the following problems, for example: the quality of output images is not sufficient; and the fixing energy required is high. Also, when wax (release agent) has been added for improving fixing ability, the toners produced by the kneading pulverizing method are cracked upon pulverization at the interfaces with the wax, so that much of the wax is disadvantageously present on the toner surface. As a result, although releasing effects can be obtained, deposition (filming) of the toners on carriers, photoconductors, and blades will easily occur. Thus, their entire performances have not been satisfactory, which is problematic.
Then, in order to overcome the above problems accompanied by the kneading pulverizing method, toner production methods based on the polymerization method have been proposed. Toners produced by the polymerization method are easily allowed to have smaller particle diameters, and their particle size distribution is sharper than that of the toners produced by the pulverization method and moreover it is possible to enclose the release agent. In one disclosed toner production method based on the polymerization method, toners are produced from elongated reaction products of urethane-modified polyesters serving as a toner binder for the purpose of improving the low temperature fixing ability and hot offset resistance (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-133665).
In addition, there are disclosed production methods for toners excellent in powder flowability and transferability when they are formed to have smaller particle diameters, as well as in all of heat resistant storage stability, low temperature fixing ability, and hot offset resistance (see, for example, JP-A Nos. 2002-287400 and 2002-351143).
Further, there are disclosed production methods for toners including an aging step for producing a toner binder having a stable molecular weight distribution to achieve both of low temperature fixing ability and hot offset resistance (see, for example, Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819).
These proposed techniques, however, do not attain a high level of low temperature fixing ability that has recently been demanded.
Then, in order to attain a high level of low temperature fixing ability, there are proposed toners containing a resin including a crystalline polyester resin, and a release agent and having a phase separation structure which is a sea-island form where the resin and wax are incompatible to each other (see, for example, JP-A No. 2004-46095).
Also, there is a proposed toner containing a crystalline polyester resin, a release agent, and a graft polymer (see, for example, JP-A No. 2007-271789).
According to these proposed techniques, a crystalline polyester resin more rapidly melts than a non-crystalline polyester resin does, which makes it possible to allow the resultant toner to have a lowered fixing temperature. Thus, it is possible to obtain a toner compatible with low temperature fixing ability and heat resistant storage stability. However, stress applied to the toner in a developing device more increases when it is used in a high-speed device, and generation of the toner aggregation and clogging of a doctor cause problems such as a void of the toner (transfer void) on the area of the outputted toner image. In addition, a toner containing a crystalline polyester resin causes problems such as generation of the toner aggregation under a high temperature and high humidity environment.
Regarding charging performance of a toner, a toner having higher charging ability has been proposed, where the toner contains a layered modified inorganic mineral, and is obtained by washing and removing an organic cation contained in the layered modified inorganic mineral of the toner (see, for example, JP-A No. 2012-118362). However, this method does not exhibit sufficient improving effects of charge rising properties, which causes problems such as toner's background smear (fogging) and toner scattering.
Accordingly, demand has arisen for a toner having low temperature fixing ability and heat resistant storage stability and further having high charging ability.